Methods And Apparatus For Controlling A Gain State Of A Wireless Receiver Operating In An Idle Mode

ABSTRACT

A technique for controlling operation of a communication subsystem is described. The subsystem is set to a first wake-up mode of operation, during which a state value from the system is read and stored in memory. The subsystem is then set to a sleep mode of operation after the first wake-up mode of operation, and to a second wake-up mode of operation after the sleep mode of operation. The stored state value is then read from the memory, where the subsystem is set to operate based on the read state value during a warm-up period of the second wake-up mode of operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of and claims priority to U.S.non-provisional patent application having application Ser. No.13/309,251 and filing date of 1 Dec. 2011, now U.S. Pat. No. ______,which is a continuation of and claims priority to U.S. non-provisionalpatent application having application Ser. No. 12/942,253 and filingdate of 9 Nov. 2010, now U.S. Pat. No. 8,116,712 B2, which is acontinuation of and claims priority to U.S. non-provisional patentapplication having application Ser. No. 12/268,011 and filing date of 10Nov. 2008, now U.S. Pat. No. 7,853,230 B2, which is a continuation ofU.S. non-provisional patent application having application Ser. No.11/065,406 and filing date of 24 Feb. 2005, now U.S. Pat. No. 7,463,872B2, each application being hereby incorporated by reference herein.

BACKGROUND

1. Field of the Technology

The present application relates generally to mobile stations operatingin wireless communication networks, and more particularly to methods andapparatus for controlling the gain states of a wireless receiveroperating in idle mode.

2. Description of the Related Art

A wireless communication device, such as a mobile station operating in awireless communication network, may provide for both voice telephony andpacket data communications. A mobile station may, for example, becompatible with 3^(rd) Generation (3G) communication standards (such asUMTS), or utilize Global System for Mobile Communications (GSM), TimeDivision Multiple Access (TDMA), or Code Division Multiple Access (CDMA)wireless network technologies.

All of these communication standards utilize radio frequency (RF) signaldetection techniques implemented in a RF receiver. A RF receiver maygenerally face three performance limiting factors: internal thermalnoise, external in-band noise, and out-of-band interference. Wheninternal thermal noise is the predominate source of interference to thedesired signal, a low receiver noise figure is desired to improvereceiver sensitivity. External in-band interference (including externalin-band noise) can also be the major source of interference; especiallywhen the out-of-band portion of the interference does not causesignificant distortion. In this case, a higher in-band dynamic range ofthe receiver is desired for good performance. The in-band dynamic rangeof the receiver is usually measured by the in-band 3^(rd) orderinterception point (i.e. “in-band IP3”). Finally, out-of-bandinterference may also result in distortions in the in-band spectrumthrough receiver non-linearities. In this case, a higher out-of-banddynamic range of the receiver is desired to improve performance. Theout-of-band dynamic range is usually measured by the out-of-band 3^(rd)order interception point (i.e. “out-of-band IP3”).

The aforementioned higher input dynamic range and lower noise figure maybe contradictory requirements since higher input dynamic range meanslower front end gain while lower noise figure suggests a higher frontend gain design. A front end that is designed to satisfy both scenarioscould be relatively expensive in cost. For a lower cost solution, somereceiver designs include a variable front end stage. In particular, alow noise amplifier (LNA) in the front end may have an adjustable gainG, which is controlled by a feedback mechanism. In such a configuration,the gain G of the LNA can be adjusted dynamically in response to thefeedback mechanism in order to trade off the noise figure with thedynamic range of the LNA when necessary.

To achieve the tradeoff, some feedback mechanisms include a leveldetector and a front end gain controller. The level detector receives aninput signal and provides a signal level or received signal strengthindicator (RSSI), and the front end gain controller receives thisindicator to generate a control signal for controlling the front endgain.

In some configurations, the above feedback mechanism in a wirelessreceiver is used not only for continuous operation mode, but also foridle mode in a mobile station application. In idle mode, in order tosave battery power, the receiver in a mobile station is turned off mostof the time; it is periodically waken up at given time slots based on apredetermined schedule, such as every 1.28, 2.56 or 5.12 seconds, toreceive message from base stations. A wake up period is usually veryshort in time, for example, about 100 ms in a CDMA2000™ mobile receiver.At the beginning of the wake up period, there is a warm-up period forsettling the receiver to a steady state.

SUMMARY

An illustrative method for controlling a gain state of a wirelessreceiver operating in an idle mode comprises the steps of receiving,during a first wake-up period of the wireless receiver, a notificationsignal which indicates that the wireless receiver is to be placed in asleep mode; reading a gain control state value from a gain controllerbased on receiving the notification signal; storing the gain controlstate value in memory; providing the stored gain control state value tothe wireless receiver during a warm-up period of a second wake-up periodfollowing the first wake-up period; and after the warm-up period of thesecond wake-up period, providing a gain control state value from thegain controller to the wireless receiver based on a signal level of acurrently received signal in the wireless receiver.

An illustrative mobile station of the present application comprises areceiver which receives radio frequency (RF) signals through an antenna,an amplifier of the receiver which is adapted to amplify the RF signals,a level detector which is adapted to detect a signal level of the RFsignals, a gain controller which is adapted to provide a gain controlstate value in response to the signal level, and a processor which isadapted to read a gain control state value from the gain controllerduring a first wake-up period of the receiver, store the gain controlstate value in memory, provide a selection signal for selecting thestored gain control state value from the memory to the receiver during awarm-up period of a second wake-up period following the first wake-upperiod, and provide a gain control state value from the gain controllerto the receiver based on a signal level of a currently received signalin the receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of present invention will now be described by way of examplewith reference to attached figures, wherein:

FIG. 1 is a block diagram that illustrates pertinent components of amobile station and a wireless communication network;

FIG. 2 is a more detailed diagram of a preferred mobile station of FIG.1;

FIG. 3 is a block diagram illustrating in further detail components ofthe mobile station of FIG. 1 used for controlling front end gain;

FIG. 4 is a graph of signals in a frequency domain before applying theknown technique of noise reduction by filtering;

FIG. 5 is a graph of signals in the frequency domain after applying theknown technique of noise reduction by filtering;

FIG. 6A is a graph of sleep and wake-up activities over time in idlemode of a wireless receiver;

FIG. 6B is an enlarged graph of the sleep and wake-up activities overtime in the wireless receiver from FIG. 6A;

FIG. 7 shows an embodiment of apparatus for controlling gain state ofthe wireless receiver operating in an idle mode to reduce settling timeduring a warm-up period of the receiver;

FIG. 8A shows a step gain control signal as a function of the receivedmean power level after the warm-up period;

FIG. 8B shows a continuous gain control signal as a function of thereceived mean power level after the warm-up period; and

FIG. 9 shows a flowchart of a method for controlling the gain state of awireless receiver operating in an idle mode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Generally, the present application provides a method and apparatus forreducing the settling time of a wireless receiver's front end gaincontrol loop. This is done by providing a previously-utilized gaincontrol state value to a low noise amplifier (LNA) of the front endduring a warm-up portion of a wake-up period of the receiver whichfollows a sleep period. At or near the end of each wake-up period, whena front end gain controller has been in steady state, a gain controlstate value of the front gain controller is read and stored in memory.During the next wake-up period, a processor retrieves the stored gaincontrol state value from the memory and applies it to the LNA of thefront end. Since the stored gain control state value was the previousoptimal value at the end of the previous wake-up period, this value maystill be optimal or near optimal for the new wake-up period. The LNAreceives this gain control state value as a “best guessed” initial gainsetting for the new wake-up period and, at such an optimal or nearoptimal gain condition, the rest of the circuitry settles relativelyquickly. At the end of the warm-up period, when the front end gaincontroller reaches steady state, the processor returns control to thefront end gain controller for the rest of the wake-up period to adjustthe gain G of the LNA based on a signal level detected by a leveldetector from a currently received signal in the wireless receiver.

On one hand, the warm-up period at the beginning of the idle modewake-up period in a radio frequency (RF) receiver and in a feedbackmechanism which includes a level detector and a front end controller ofthe RF receiver should be sufficiently long (e.g. 20 milliseconds) toensure that the receiver has enough time to reach an optimal receivingcondition. On the other hand, the warm-up period should be as short aspossible to conserve battery power. The front end gain controller reactsto both the desired input signal and interference, and settles at anoptimal receiving state. Ideally, this optimal state produces a properoutput signal to control the front end gain, resulting in an optimaltradeoff between dynamic range and noise figure for the current inputsignal condition. However, during the warm-up period and before thefront end controller settles to its optimal receiving state, the frontend gain controller may generate uncertain and possibly random states.Thus, the controlled LNA may not be optimized during the warm-up period.For example, when the LNA requires a high gain for optimal reception ata given input signal condition, the front end gain controller mayerroneously be in a low gain state during the warm up period, which maycause a higher noise figure and may generate a higher thermal noiselevel. Similarly, when the LNA requires a low gain for optimal receptionat a given condition, the front end gain controller may erroneously bein a high gain state, resulting in a lower IP3 and consequently higherintermodulation distortion (IMD).

Therefore, embodiments of a method and apparatus which control the frontend gain state of a wireless receiver during wake-up periods in idlemode so as to minimize the settling time are provided herein.

FIG. 1 is a block diagram of a communication system 100, that includes amobile station 102, which communicates through a wireless communicationnetwork 104. Mobile station 102 preferably includes a visual display112, a keyboard 114, and perhaps one or more auxiliary user interfaces(UI) 116, each of which is coupled to a controller 106. Controller 106is also coupled to radio frequency (RF) transceiver circuitry 108 and anantenna 110. Typically, controller 106 is embodied as a centralprocessing unit (CPU), which runs operating system software in a memorycomponent (not shown). Controller 106 will normally control overalloperation of mobile station 102, whereas signal-processing operationsassociated with communication functions are typically performed in RFtransceiver circuitry 108. Controller 106 interfaces with device display112 to display received information, stored information, user inputs,and the like. Keyboard 114, which may be a telephone type keypad or fullalphanumeric keyboard, is normally provided for entering data forstorage in mobile station 102, information for transmission to network104, a telephone number to place a telephone call, commands to beexecuted on mobile station 102, and possibly other or different userinputs.

Mobile station 102 sends communication signals to and receivescommunication signals from network 104 over a wireless link via antenna110. RF transceiver circuitry 108 performs functions similar to those ofa radio network (RN) 128, including for example modulation/demodulationand possibly encoding/decoding and encryption/decryption. It is alsocontemplated that RF transceiver circuitry 108 may perform certainfunctions in addition to those performed by RN 128. It will be apparentto those skilled in art that RF transceiver circuitry 108 will beadapted to particular wireless network or networks in which mobilestation 102 is intended to operate.

Mobile station 102 includes a battery interface 122 for receiving one ormore rechargeable batteries 124. Battery 124 provides electrical powerto electrical circuitry in mobile station 102, and battery interface 122provides for a mechanical and electrical connection for battery 124.Battery interface 122 is coupled to a regulator 126, which regulatespower to the device, providing an output having a regulated voltage V.Mobile station 102 also operates using a memory module 120, such as aSubscriber Identity Module (SIM) or a Removable User Identity Module(R-UIM), which is connected to or inserted in mobile station 102 at aninterface 118.

Mobile station 102 may consist of a single unit, such as a datacommunication device, a cellular telephone, a multiple-functioncommunication device with data and voice communication capabilities, apersonal digital assistant (PDA) enabled for wireless communication, ora computer incorporating an internal modem. Alternatively, mobilestation 102 may be a multiple-module unit comprising a plurality ofseparate components, including but in no way limited to a computer orother device connected to a wireless modem. In particular, for example,in the mobile station block diagram of FIG. 1, RF transceiver circuitry108 and antenna 110 may be implemented as a radio modem unit that may beinserted into a port on a laptop computer. In this case, the laptopcomputer would include display 112, keyboard 114, one or more auxiliaryUIs 116, and controller 106 embodied as the computer's CPU. It is alsocontemplated that a computer or other equipment not normally capable ofwireless communication may be adapted to connect to and effectivelyassume control of RF transceiver circuitry 108 and antenna 110 of asingle-unit device such as one of those described above. Such a mobilestation 102 may have a more particular implementation as described laterin relation to mobile station 202 of FIG. 2.

Mobile station 102 communicates in and through wireless communicationnetwork 104. In the embodiment of FIG. 1, wireless network 104 is aThird Generation (3G) supported network based on Code Division MultipleAccess (CDMA) technologies. In particular, wireless network 104 is aCdma2000™ network which includes fixed network components coupled asshown in FIG. 1. Cdma2000™ is a trademark of the TelecommunicationsIndustry Association (TIA). Wireless network 104 of the Cdma2000-typeincludes a Radio Network (RN) 128, a Mobile Switching Center (MSC) 130,a Signaling System 7 (SS7) network 140, a Home LocationRegister/Authentication Center (HLR/AC) 138, a Packet Data Serving Node(PDSN) 132, an IP network 134, and a Remote Authentication Dial-In UserService (RADIUS) server 136. SS7 network 140 is communicatively coupledto a network 142 (such as a Public Switched Telephone Network or PSTN),whereas IP network is communicatively coupled to a network 144 (such asthe Internet).

During operation, mobile station 102 communicates with RN 128, whichperforms functions such as call-setup, call processing, and mobilitymanagement. RN 128 includes a plurality of base station transceiversystems that provide wireless network coverage for a particular coveragearea commonly referred to as a “cell”. A given base station transceiversystem of RN 128, such as the one shown in FIG. 1, transmitscommunication signals to and receives communication signals from mobilestations within its cell. The base station transceiver system normallyperforms such functions as modulation and possibly encoding and/orencryption of signals to be transmitted to the mobile station inaccordance with particular, usually predetermined, communicationprotocols and parameters, under control of its controller. The basestation transceiver system similarly demodulates and possibly decodesand decrypts, if necessary, any communication signals received frommobile station 102 within its cell. Communication protocols andparameters may vary between different networks. For example, one networkmay employ a different modulation scheme and operate at differentfrequencies than other networks. The underlying services may also differbased on its particular protocol revision.

The wireless link shown in communication system 100 of FIG. 1 representsone or more different channels, typically different radio frequency (RF)channels, and associated protocols used between wireless network 104 andmobile station 102. An RF channel is a limited resource that must beconserved, typically due to limits in overall bandwidth and a limitedbattery power of mobile station 102. Those skilled in art willappreciate that a wireless network in actual practice may includehundreds of cells depending upon desired overall expanse of networkcoverage. All pertinent components may be connected by multiple switchesand routers (not shown), controlled by multiple network controllers.

For all mobile station's 102 registered with a network operator,permanent data (such as mobile station 102 user's profile) as well astemporary data (such as mobile station's 102 current location) arestored in a HLR/AC 138. In case of a voice call to mobile station 102,HLR/AC 138 is queried to determine the current location of mobilestation 102. A Visitor Location Register (VLR) of MSC 130 is responsiblefor a group of location areas and stores the data of those mobilestations that are currently in its area of responsibility. This includesparts of the permanent mobile station data that have been transmittedfrom HLR/AC 138 to the VLR for faster access. However, the VLR of MSC130 may also assign and store local data, such as temporaryidentifications. HLR/AC 138 also authenticates mobile station 102 onsystem access.

In order to provide packet data services to mobile station 102 in aCdma2000-based network, RN 128 communicates with PDSN 132. PDSN 132provides access to the Internet 144 (or intranets, Wireless ApplicationProtocol (WAP) servers, etc.) through IP network 134. PDSN 132 alsoprovides foreign agent (FA) functionality in mobile IP networks as wellas packet transport for virtual private networking. PDSN 132 has a rangeof IP addresses and performs IP address management, session maintenance,and optional caching. RADIUS server 136 is responsible for performingfunctions related to authentication, authorization, and accounting (AAA)of packet data services, and may be referred to as an AAA server.

Those skilled in the art will appreciate that wireless network 104 maybe connected to other systems, possibly including other networks, notexplicitly shown in FIG. 1. A network will normally be transmitting atvery least some sort of paging and system information on an ongoingbasis, even if there is no actual packet data exchanged. Although thenetwork consists of many parts, these parts all work together to resultin certain behaviours at the wireless link.

FIG. 2 is a detailed block diagram of a preferred mobile station 202utilized in the present application. Mobile station 202 is preferably atwo-way communication device having at least voice and advanced datacommunication capabilities, including the capability to communicate withother computer systems. Depending on the functionality provided bymobile station 202, it may be referred to as a data messaging device, atwo-way pager, a cellular telephone with data messaging capabilities, awireless Internet appliance, or a data communication device (with orwithout telephony capabilities). Mobile station 202 may communicate withany one of a plurality of base station transceiver systems 200 withinits geographic coverage area.

Mobile station 202 will normally incorporate a communication subsystem211, which includes a receiver 212, a transmitter 214, and associatedcomponents, such as one or more (preferably embedded or internal)antenna elements 216 and 218, local oscillators (LOs) 213, and aprocessing module such as a digital signal processor (DSP) 220.Communication subsystem 211 is analogous to RF transceiver circuitry 108and antenna 110 shown in FIG. 1. As will be apparent to those skilled infield of communications, particular design of communication subsystem211 depends on the communication network in which mobile station 202 isintended to operate.

Mobile station 202 may send and receive communication signals over thenetwork after required network registration or activation procedureshave been completed. Signals received by antenna 216 through the networkare input to receiver 212, which may perform such common receiverfunctions as signal amplification, frequency down conversion, filtering,channel selection, and, analog-to-digital (A/D) conversion. A/Dconversion of a received signal allows more complex communicationfunctions such as demodulation and decoding to be performed in DSP 220.In a similar manner, signals to be transmitted are processed, includingmodulation and encoding, for example, by DSP 220. These DSP-processedsignals are input to transmitter 214 for digital-to-analog (D/A)conversion, frequency up conversion, filtering, amplification andtransmission over communication network via antenna 218. DSP 220 notonly processes communication signals, but also provides for receiver andtransmitter control. For example, the gains applied to communicationsignals in receiver 212 and transmitter 214 may be adaptively controlledthrough automatic gain control algorithms implemented in DSP 220.

Network access is associated with a subscriber or user of mobile station202, and therefore mobile station 202 requires a memory module 262, suchas a Subscriber Identity Module or “SIM” card or a Removable UserIdentity Module (R-UIM), to be inserted in or connected to an interface264 of mobile station 202 in order to operate in the network. Sincemobile station 202 is a mobile battery-powered device, it also includesa battery interface 254 for receiving one or more rechargeable batteries256. Such a battery 256 provides electrical power to most if not allelectrical circuitry in mobile station 202, and battery interface 254provides for a mechanical and electrical connection for it. Batteryinterface 254 is coupled to a regulator (not shown) which regulatespower to all of the circuitry, providing an output having a regulatedvoltage V.

Microprocessor 238, which is one implementation of controller 106 ofFIG. 1, controls overall operation of mobile station 202. This controlincludes network selection techniques of the present application.Communication functions, including at least data and voicecommunications, are performed through communication subsystem 211.Microprocessor 238 also interacts with additional device subsystems suchas a display 222, a flash memory 224, a random access memory (RAM) 226,auxiliary input/output (I/O) subsystems 228, a serial port 230, akeyboard 232, a speaker 234, a microphone 236, a short-rangecommunications subsystem 240, and any other device subsystems generallydesignated at 242. Some of the subsystems shown in FIG. 2 performcommunication-related functions, whereas other subsystems may provide“resident” or on-device functions. Notably, some subsystems, such askeyboard 232 and display 222, for example, may be used for bothcommunication-related functions, such as entering a text message fortransmission over a communication network, and device-resident functionssuch as a calculator or task list. Operating system software used bymicroprocessor 238 is preferably stored in a persistent store such asflash memory 224, which may alternatively be a read-only memory (ROM) orsimilar storage element (not shown). Those skilled in the art willappreciate that the operating system, specific device applications, orparts thereof, may be temporarily loaded into a volatile store such asRAM 226.

Microprocessor 238, in addition to its operating system functions,preferably enables execution of software applications on mobile station202. A predetermined set of applications, which control basic deviceoperations, including at least data and voice communicationapplications, will normally be installed on mobile station 202 duringits manufacture. A preferred application that may be loaded onto mobilestation 202 may be a personal information manager (PIM) applicationhaving the ability to organize and manage data items relating to usersuch as, but not limited to, e-mail, calendar events, voice mails,appointments, and task items. Naturally, one or more memory stores areavailable on mobile station 202 and SIM 256 to facilitate storage of PIMdata items and other information.

The PIM application preferably has the ability to send and receive dataitems via the wireless network. In a preferred embodiment, PIM dataitems are seamlessly integrated, synchronized, and updated via thewireless network, with the mobile station user's corresponding dataitems stored and/or associated with a host computer system therebycreating a mirrored host computer on mobile station 202 with respect tosuch items. This is especially advantageous where the host computersystem is the mobile station user's office computer system. Additionalapplications may also be loaded onto mobile station 202 through network,an auxiliary I/O subsystem 228, serial port 230, short-rangecommunications subsystem 240, or any other suitable subsystem 242, andinstalled by a user in RAM 226 or preferably a non-volatile store (notshown) for execution by microprocessor 238. Such flexibility inapplication installation increases the functionality of mobile station202 and may provide enhanced on-device functions, communication-relatedfunctions, or both. For example, secure communication applications mayenable electronic commerce functions and other such financialtransactions to be performed using mobile station 202.

In a data communication mode, a received signal such as a text message,an e-mail message, or web page download will be processed bycommunication subsystem 211 and input to microprocessor 238.Microprocessor 238 will preferably further process the signal for outputto display 222 or alternatively to auxiliary I/O device 228. A user ofmobile station 202 may also compose data items, such as e-mail messages,for example, using keyboard 232 in conjunction with display 222 andpossibly auxiliary I/O device 228. Keyboard 232 is preferably a completealphanumeric keyboard and/or telephone-type keypad. These composed itemsmay be transmitted over a communication network through communicationsubsystem 211.

For voice communications, the overall operation of mobile station 202 issubstantially similar, except that the received signals would be outputto speaker 234 and signals for transmission would be generated bymicrophone 236. Alternative voice or audio I/O subsystems, such as avoice message recording subsystem, may also be implemented on mobilestation 202. Although voice or audio signal output is preferablyaccomplished primarily through speaker 234, display 222 may also be usedto provide an indication of the identity of a calling party, period of avoice call, or other voice call related information, as some examples.

Serial port 230 in FIG. 2 is normally implemented in a personal digitalassistant (PDA)-type communication device for which synchronization witha user's desktop computer is a desirable, albeit optional, component.Serial port 230 enables a user to set preferences through an externaldevice or software application and extends the capabilities of mobilestation 202 by providing for information or software downloads to mobilestation 202 other than through a wireless communication network. Thealternate download path may, for example, be used to load an encryptionkey onto mobile station 202 through a direct and thus reliable andtrusted connection to thereby provide secure device communication.

Short-range communications subsystem 240 of FIG. 2 is an additionaloptional component, which provides for communication between mobilestation 202 and different systems or devices, which need not necessarilybe similar devices. For example, subsystem 240 may include an infrareddevice and associated circuits and components, or a Bluetooth™communication module to provide for communication with similarly enabledsystems and devices. Bluetooth™ is a registered trademark of BluetoothSIG, Inc.

FIG. 3 is a block diagram illustrating in further detail receivercomponents of receiver 212. Receiver components of receiver 212 of FIG.3 include a front end stage 302, a down converter 304, a filter 306, andan intermediate frequency (IF) and/or baseband stage 308. Front endstage 302 typically includes a filter 310, a low noise amplifier (LNA)312, and a filter 314. Filter 310 of front end stage 302 has an inputcoupled to antenna 216 and an output coupled to an input of LNA 312. LNA312 has an output coupled to an input of filter 314, which has an output322 coupled to an input of down converter 304. Down converter 304 has anoutput 324 coupled to an input of filter 306. An output 325 of filter306 is coupled to an input of IF/baseband stage 308, which has an output326 coupled to DSP 220.

In front end stage 302, filters 310 and 314 are bandpass filterstypically using Surface Acoustic Wave (SAW) filter technology. Thefunction of down converter 304 is to mix the RF signals received throughfront end stage 302 with a local oscillator (LO) in down converter 304,to thereby produce IF signals (or baseband signals if zero IF technologyis utilized). The function of IF/baseband stage 308 is to convert the IFsignals into baseband signals (unless zero IF technology is utilized)and to process and/or filter the baseband signals. The IF/baseband stage308 usually also provides automatic gain control (AGC) functionality,which adjusts the gain of the IF/baseband stage 308 to ensure the totalsignal, interference, noise and distortion level seen at signal 326remains unchanged, regardless of changes in input signal andinterference levels, and how the front end gain 312 changes which willbe further discussed hereinafter. Filter 306 may be part of IF/baseband308. When IF is used, filter 306 is typically a bandpass filter; whenzero IF is used, filter 306 is typically a low pass filter. When IF isused, it is possible that filter 306 is implemented in multiple stages;for example, a bandpass filter in the IF stage and a lowpass filter atthe baseband stage. DSP 220 operates to process the baseband signals,for example, to correlate the baseband signals with a predeterminedsignal under control of microprocessor 238.

FIG. 4 is a graph 400 showing curves in the frequency domain at output322 and/or output 324 in transceiver 212 (although outputs 322 and 324are associated with different frequency ranges). In graph 400, a curve402 depicts the desired received signal, a curve 406 depicts internalnoise as well as external interference, curves 408 and 410 depict strongnarrow out-of-band interference, and curves 412 and 414 depictintermodulation distortion produced in front end stage 302 due toundesirable non-linearity. A curve 404 depicts the shape of a responseof filter 306 that follows, which is intended to remove the out-of-bandinterference and distortion. FIG. 5 is a graph 500 of curves in thefrequency domain at output 325 and/or output 326 in receiver 212(although outputs 325 and 326 may be associated with different frequencyranges). Note that curve 406 of FIG. 5 depicting the internal noise andexternal interference after filtering becomes shaped similarly tofilter's 306 response (i.e. curve 404 of FIG. 4). As illustrated, theout-of-band contents (by comparing curve 406 of FIG. 4) are greatlyreduced. Out-of-band interferences and intermodulation distortion (i.e.curves 408 and 410 as well as 412 of FIG. 4) are also greatly reduced.Intermodulation distortion (i.e. curve 414) may still exist.

In order to improve processing due to the trade-off in noise figure anddynamic range requirements, some receiver designs include a variablefront end stage. In particular, referring back to FIG. 3, LNA 312 has anadjustable gain G which is controlled by a variable gain control signal320 from a feedback mechanism. In general, the gain G of LNA 312 isadjusted dynamically in response to the feedback mechanism in order totrade off the noise figure with the dynamic range of LNA 312 whennecessary. LNA 312 has an inherent limited dynamic range due to itsimperfect linearity.

In general, variable gain control signal 320 is produced by a front endgain controller 332 based on an output of level detector 316 which isinput to LNA 312 for controlling the gain G. Level detector 316 operatesto detect an overall level of an input signal 318 which is the totaldesired signal plus interference and distortion. Front end gaincontroller 332 maps the output 319 of level detector 316 to the variablegain control signal 320. During operation, level detector 316continually monitors the total desired signal plus interference anddistortion. When the signal level is high, for example, the frond endgain controller causes the variable gain control signal 320 to reducethe adjustable gain G to LNA 312. The reason is that, in this situation,receiver 212 requires a higher dynamic range since the noise figure isless important.

Level detector 316 receives input signal 318 from one of a few differentsources, depending on which prior art technique is utilized. One sourceis from output 322 of front end stage 302, another source is from output324 of down converter 304, and yet another source is from output 326where level detector 316 is included in the signal processing of DSP220.

FIG. 6A shows sleep and wake-up activities over time during idle modeoperation, where a high value indicates that the receiver is in awake-up period and a low value indicates that the receiver is in a sleepperiod. The receiver may be receiver 212 of FIG. 3, utilized in thedevices of FIGS. 1-2. In idle mode, receiver 212 sleeps and wakes uprepeatedly. Receiver 212 is placed in a sleep mode (i.e. a low powermode such as being turned off) where it does not receive signals, butdoes receives signals when it wakes up. Waveform 610 shows a firstwake-up period where receiver 212 wakes up to receive signals. Waveform620 shows a second wake-up period following after the first wake-upperiod.

FIG. 6B shows magnified views of two consecutive wake-up periods 610 and620 from FIG. 6A during idle mode operation of the receiver. As shown byperiods 610 and 620, a time instant A1 and a time instant A2 are thestart of wake-up period 610 and the start of wake-up period 620,respectively. At these time instants, receiver 212 is turned on andbegins to “warm-up”. Period B1 and period B2 are warm-up periods, whichare the actual or maximum time periods it takes for the circuitry tosettle into steady state. A time instant E1 and a time instant E2 arethe end of warm-up period B1 and the end of warm-up period B2,respectively. A time instant D1 and a time instant D2 are the end ofwake-up period 610 and the end of wake-up period 620, respectively. Atime instant C1 and a time instant C2 are time points prior to the endsof the wake-up periods, respectively, and most preferably are the timepoints immediately before the ends of the wake-up periods. During thewarm-up periods B1 and B2, receiver 212 has not settled into a steadystate mode of operation, and the front end gain state is uncertain andmay in fact be random.

FIG. 7 shows an embodiment of the apparatus for controlling a gain stateof a wireless receiver in an idle mode to reduce settling time duringwarm-up periods according to the present application. As shown in FIG.7, receiver 212 is similar to that of FIG. 3 but includes additionalcomponents and techniques. The apparatus as shown further includes alevel detector 710, a front end gain controller 720, a decoder 725, amultiplexer 730, memory 740, and a timer 750. Level detector 710 andfront end gain controller 720 may be incorporated in DSP 705 orimplemented separately if desired. Similarly, memory 740 and timer 750may be incorporated in microprocessor 738 or implemented separately ifdesired.

Level detector 710 receives an input signal 326 from receiver 212 todetect a mean power level of the input signal and produces an inputsignal mean power level indicator signal or RSSI 327 to front end gaincontroller 720. During warm-up periods B1 and B2 of FIG. 6 b, front endgain controller 720 has not settled into steady state and an uncertainor random signal 328 may be produced. Thus, if signal 328 is used tocontrol LNA 312 directly during the warm-up period, LNA 312 may not beadjusted to a proper gain during this period of time. Instead of usingsignal 328 during the warm-up period, however, a multiplexer 730 isselected by microprocessor 738 to provide a better initial value 329from memory 740 and made available at port B. The generation of thisinitial value 329 and the control method will be described in furtherdetail in the following paragraph. Subsequently, during a period frominstant E1 to instant D1 or from instant E2 to D2 (FIG. 6B) (wake-upperiods), front end gain controller 720 has settled to steady state andtherefore signal 328 can be used to properly control LNA 312 during thistime.

Once decoding operation of decoder 725 has finished during a wake-upperiod, decoder 725 provides a notification signal to microprocessor 738which indicates decoding has finished. Receiver 212 is ready to beplaced in a sleep mode of operation where it may be placed in a lowpower state or powered down. At instant C1 immediately before instant D1which marks the end of the first wake-up period 610 (FIG. 6B),microprocessor 738 reads a gain control state value from front end gaincontroller 720 and stores it into memory 740. Memory 740 may beimplemented as random access memory (RAM), for example. When receiver212 is in the next wake-up period 620, during the warm-up period B2(FIG. 6B), microprocessor 738 sets the state value selection signal 330to inhibit the input terminal A of multiplexer 730 and provide the inputterminal B of multiplexer 730 at the MUX 730 output, to thereby providethe gain control state value 329 to the gain control terminal of LNA312. The same method may be used repeatedly for each and every wake-upperiod, except the very first wake-up after the mobile station ispowered up which will be addressed hereinafter. By this method, the gainG of LNA 312 is adjusted to a statistically-appropriate initial statevalue during warm-up periods, in accordance with the gain control statevalue that was optimal a short time period beforehand at the end ofprevious wake-up period.

When receiver 212, level detector 710, and front end gain controller 720operate in steady state (such as from instant E2 to instant D2 of FIG.6B), front end gain controller 720 receives a mean power level (RSSI)signal 327 and provides a gain control state value 328. This gaincontrol state value may be one selected from that depicted in FIG. 8A.Timer 750 of the apparatus is set to time a period from the end of thefirst wake-up period 610 to the beginning of the second wake-up period620. Timer 750 is also set at the beginning of the wake-up slot (such asA2) and expires after a period that is equal to the warm-up period (suchas B2, at a time instant such as E2). At this time, timer 750 triggersthe microprocessor 738 to set the state value selection signal 330 toprovide the input terminal A of multiplexer 730 and not the inputterminal B of multiplexer 730 at its output. The gain control statevalue 328 is sent to LNA 312 from front end gain controller 720. Thegain G of LNA 312 is adjusted according to the gain control state value,which is optimal by design and based on the signal level of thecurrently received signal.

Thus, the described method relies on a “settled” gain state value fromthe previous wake-up period. In the very first wake-up period after themobile station is powered up, however, there is no recent settled valueto use and therefore an optimal initial guess is not available. Thereceiver may have to suffer a possibly longer settling time for thisfirst wake-up period. However, this does not degrade performancesignificantly because when the receiver is powered up, the mobilestation is in its system determination state during which it issearching for an available wireless network. This process takes muchlonger than a slotted mode wake-up period, thus the longer settling timecaused by the imperfect initial estimate has little impact onperformance during this time. Two options can be used for the very firstwake-up period: one is to use the signal 328 directly to control LNA 312by selecting port A at multiplexer 330; and the other is to use theinitial state value that is stored in memory 740 (e.g. either apredetermined default state value or a state value obtained duringprevious wake-up period before last power down).

In designing a variable gain receiver front end for trading off betweennoise figure and dynamic range, there are three options: (1) an N-stepvariable gain, such as a two-step gain design with a high gain and a lowgain; a three-step gain design with a high gain, a medium gain, and alow gain; an N-step gain design with a plurality of gain state values,etc.; (2) a continuously variable gain that can set the gain in acontinuous range; and (3) a combination of step gain and a continuouslyvariable gain. Accordingly, the front gain controller 720 needs toprovide the corresponding control signal 328.

In a first embodiment of the present application, the receiver uses stepgain control; the control characteristics of front end gain controller720 is shown in FIG. 8A, which utilizes a three-step gain control as anembodiment. When the receive mean power level or RSSI is less than R1,the receive signal is weak and thus LNA 312 requires a high gain.Therefore, front end gain controller 720 provides a high gain controlstate value for LNA 312. When the receive mean power level or RSSI isabove F1 and below R2, front end gain controller 720 provides a mediumgain control state value to LNA 312 so that the gain G of LNA 312 isadjusted to a medium gain. When the receive mean power level or RSSI isbetween R1 and F1, LNA 312 can provide good performance either at highgain or medium gain, the controller determines the output stateaccording to a hysteresis rule based on the history of the gain stateapplied to LNA 312. The hysteresis rule may follow the following logic:if the gain state was high, it continues to stay high; if the gain wasmedium, it continues to stay medium; etc. The hysteresis rule preventsthe gain state jumps back and forth too quickly and frequently whenreceived signal strength varies around the thresholds. When the receivemean power level or amplitude is above F2, the signal is strong;therefore front end gain controller 720 provides a low gain controlsignal to LNA 312 so that LNA 312 is at low gain. The low gain may beimplemented by bypassing some or all stages of the LNA. When the receivemean power level or RSSI is between R2 and F2, the LNA 312 can providegood performance either at medium gain or low gain, the controllerdetermines the output state using the hysteresis rule: if the gain statewas medium, it continues to stay medium; if the gain was low, itcontinues to stay low.

With respect to the “two-step” gain design having a high gain and a lowgain, the gain state is a high gain control state value while thereceive mean power level is less than a first threshold R1; the gainstate is a low gain control state value while the receive mean powerlevel is more than a second threshold F1; and the gain state is subjectto the hysteresis rule between a high gain control state value and a lowgain control state value while the receive mean power level is betweenR1 and F1.

In the second embodiment of the present application, the receiver usescontinuously-variable gain control. In this case, front end gaincontroller 720 provides a continuously variable gain control signal asshown in FIG. 8B. In FIG. 8B, when the receive mean power level or RSSIis low, front end gain controller 720 provides a high gain control statevalue so that LNA 312 is adjusted to a high gain. When the receive meanpower level increases, front end gain controller 720 adjusts the gainstate values so as to lower the gain G of LNA 312. The relation betweenthe gain control state value and the receive mean power level may benonlinear, and desirably is a monotonically non-increasing function suchas that shown.

In the third embodiment of the present application, the receiver usesboth step and continuously variable gain control. Front end gaincontroller 720 provides step and continuously variable gain controlsignals, and the signal lines 328, 329, and 331 of FIG. 7 areinterpreted as multiple parallel lines or an array of signals. At leastone signal line corresponds to step gain control and the other signallines corresponds to continuous gain control. LNA 312 may be controlledby both types of control signals simultaneously. For example, one stageof LNA 312 receives a step gain control signal and another stage of itreceives a continuous gain control signal.

FIG. 9 shows a flowchart of a method for controlling gain state of thewireless receiver operating in an idle mode according to the presentapplication. At step 805 of FIG. 9, the decoder 725 of the mobile deviceprovides a notification signal to notify the microprocessor 738 that thedecoder has finished decoding the signal in a wake-up period. Thissignal indicates that the receiver is ready to be placed in a sleepmode, so microprocessor 738 can turn off power of the receiver 212(e.g., at time instants D1, D2, etc. of FIG. 6B). At step 808, inresponse to the notification from decoder 725, the microprocessor 328reads the gain state 328 and stores it in memory 740. It also sets timer750 to a period from the end of a first wake-up period (such as instantD1 of FIG. 6B) to the beginning of a second wake-up period (such asinstant A2 of FIG. 6B) for the next wake up time. Receiver 212 is placedin the sleep mode (e.g. receiver 212 is powered off).

At step 810, when timer 750 expires and informs microprocessor 738 ofthe start of the wake-up period (e.g. instants A1, A2, etc. of FIG. 6B),the microprocessor 738 turns on the receiver 212 and sets timer 750 to aperiod equal to the warm-up period (e.g. B1 or B2 of FIG. 6B) to startcounting. The microprocessor 738 also sets the MUX 730 to select theport B to use gain state value 329 from memory. At step 815, timer 750expires and notifies the microprocessor 738 of the end of the warm-upperiod (e.g. instants E1 and E2 of FIG. 6B). In response to thisnotification, the microprocessor 738 sets the MUX 730 through selectionsignal 330 to allow the path from front end gain controller 720 to LNA312 via port A of MUX 730. Gain control state value 328 is provided toLNA 312 from front end gain controller 720, which operates based on asignal level of currently received signals. At step 820, themicroprocessor 738 detects whether the decoder 725 notification offinishing decoding has arrived; if not it continues to detect, if sooperation goes back to step 805.

Advantageously, the present application provides a method and apparatusfor controlling a gain state of a wireless receiver to achieve fastersettling time during wake-up periods in idle mode. One illustrativemethod includes the steps of receiving a notification signal whichindicates that the wireless receiver is to be placed in a sleep mode,reading a gain control state value from a gain controller based onreceiving the notification signal, storing the gain control state valuein memory, providing the stored gain control state value from the memoryto the wireless receiver during a warm-up period of a second wake-upperiod following the first wake-up period, and providing a gain controlstate value from the gain controller to the wireless receiver based on areceived signal level of a currently received signal of the wirelessreceiver after the warm-up period.

An illustrative mobile station of the present application comprises areceiver which receives radio frequency (RF) signals through an antenna,an amplifier of the receiver which is adapted to amplify the RF signals,a level detector which is adapted to detect a signal level of the RFsignals, a gain controller which is adapted to provide a gain controlstate value in response to the signal level, and a processor which isadapted to read a gain control state value from the gain controllerduring a first wake-up period of the receiver, store the gain controlstate value in memory, provide a selection signal for selecting thestored gain control state value from the memory to the receiver during awarm-up period of a second wake-up period following the first wake-upperiod, and provide a gain control state value from the gain controllerto the receiver based on a signal level of a currently received signalin the receiver.

An illustrative circuit for a wireless receiver may comprise a low noiseamplifier (LNA) which is adapted to amplify radio frequency (RF) signalsin the wireless receiver; a level detector which is adapted to detect asignal level of the RF signals; a gain controller which is adapted toprovide a gain control state value in response to the signal level; anda processor which is adapted to read a gain control state value from thegain controller during a first wake-up period of the wireless receiver,store the gain control state value in memory, provide a selection signalfor selecting the stored gain control state value from the memory duringa warm-up period of a second wake-up period following the first wake-upperiod, and provide after the warm-up period of the second wake-upperiod a gain control state value from the gain controller to thewireless receiver based on a signal level of a currently received signalin the wireless receiver.

The above-described embodiments of the present application are intendedto be examples only. Those of skill in the art may effect alterations,modifications and variations to the particular embodiments withoutdeparting from the scope of the application. The invention describedherein in the recited claims intends to cover and embrace all suitablechanges in technology.

1. A method for controlling operation of a communication subsystem, themethod comprising: setting the communication subsystem to a firstwake-up mode of operation; reading a state value from the communicationsystem during the first wake-up mode of operation and storing the statevalue in memory; setting the communication subsystem to a sleep mode ofoperation after the first wake-up mode of operation; setting thecommunication subsystem to a second wake-up mode of operation after thesleep mode of operation; and reading from the memory the stored statevalue, and setting the communication subsystem to operate based on theread state value during a warm-up period of the second wake-up mode ofoperation.
 2. The method of claim 1, further comprising: after thewarm-up period, setting the communication subsystem to operate based ona current state value of the communication subsystem in the secondwake-up mode of operation after the warm-up period.
 3. The method ofclaim 2, wherein the current state value is based on a detected signallevel of a current signal received in the communication subsystem. 4.The method of claim 3, wherein the signal received in the communicationsubsystem comprises a radio frequency (RF) signal.
 5. The method claim1, further comprising: running a sleep mode timer for the sleep mode ofoperation; and in response to expiration of the sleep mode timer,setting the communication subsystem to the second wake-up mode ofoperation.
 6. The method of claim 1, wherein the communication subsystemcomprises a radio frequency (RF) receiver.
 7. The method of claim 1,wherein the communication subsystem comprises a radio frequency (RF)receiver, and wherein the act of setting the communication subsystem tooperate based on the stored state value comprises providing the storedstate value to an amplifier of the RF receiver.
 8. The method of claim1, wherein the state value is one of a plurality of N state values. 9.The method of claim 1, wherein a communication device having thecommunication subsystem comprises a mobile station configured to operatein a wireless communication network.
 10. An electrical circuit,comprising; a processor; memory coupled to the processor; acommunication subsystem coupled to the processor; a level detectorconfigured to detect a signal level of a signal received in thecommunication subsystem; a state controller configured to provide one ofa plurality of state values in response to the detected signal levelfrom the level detector; the processor being configured to: set thecommunication subsystem to a first wake-up mode of operation; read astate value from the state controller during the first wake-up mode ofoperation and store the state value in the memory; set the communicationsubsystem to a sleep mode of operation after the first wake-up mode ofoperation; set the communication subsystem to a second wake-up mode ofoperation after the sleep mode of operation; and read from the memorythe stored state value, and set the communication subsystem to operatebased on the read state value during a warm-up period of the secondwake-up mode of operation.
 11. The electrical circuit of claim 10,wherein the processor is further configured to: after the warm-upperiod, set the communication subsystem to operate based on a currentstate value of the communication subsystem in the second wake-up mode ofoperation after the warm-up period.
 12. The electrical circuit of claim11, wherein the current state value is based on a current signal levelfrom the level detector.
 13. The electrical circuit of claim 12, whereinthe signal comprises a radio frequency (RF) signal.
 14. The electricalcircuit of claim 10, wherein the processor is further configured to: runa sleep mode timer for the sleep mode of operation; and in response toexpiration of the sleep mode timer, setting the communication subsystemto the second wake-up mode of operation.
 15. The electrical circuit ofclaim 10, wherein the communication subsystem comprises a wirelessreceiver.
 16. The electrical circuit of claim 10, wherein thecommunication subsystem comprises a wireless receiver, and whereinsetting the communication subsystem to operate based on the stored statevalue comprises providing the stored state value to an amplifier of thewireless receiver.
 17. A communication device, comprising: a processor;memory coupled to the processor; a communication subsystem coupled tothe processor; a level detector configured to detect a signal level of asignal received in the communication subsystem; a state controllerconfigured to provide one of a plurality of state values in response tothe detected signal level from the level detector; the processor beingconfigured to: set the communication subsystem to a first wake-up modeof operation; read a state value from the state controller during thefirst wake-up mode of operation and store the state value in the memory;set the communication subsystem to a sleep mode of operation after thefirst wake-up mode of operation; set the communication subsystem to asecond wake-up mode of operation after the sleep mode of operation; andread from the memory the stored state value, and set the communicationsubsystem to operate based on the read state value during a warm-upperiod of the second wake-up mode of operation.
 18. The communicationdevice of claim 17, wherein the processor is further configured to:after the warm-up period, set the communication subsystem to operatebased on a current state value of the communication subsystem in thesecond wake-up mode of operation after the warm-up period.
 19. Thecommunication device of claim 18, wherein the current state value isbased on a current signal level from the level detector.
 20. Thecommunication device of claim 19, wherein the signal comprises a radiofrequency (RF) signal.